The prior art vehicular exhaust muffler typically is an elongated structure with a constant oval or circular cross section along its length. The exterior of this prior art exhaust muffler includes one or more sheets of metal wrapped into an oval or circular cross-section and secured by a longitudinally extending seam.
The internal components of the prior art exhaust muffler comprise a plurality of parallel tubes supported by transverse baffles having generally the same oval or circular shape as the wrapped outer shell. The baffles meet the inner surface of the wrapped outer shell to define chambers within the muffler. Portions of certain tubes in the prior art muffler are perforated to permit a controlled flow of exhaust gases into or out of the chambers.
A pair of heads are mechanically connected to the opposed longitudinal ends of the wrapped outer shell to enclose the prior art muffler. The two heads have a total of at least two apertures extending therethrough. Short longitudinally extending tubular nipples extend through the apertures in the heads of the prior art muffler to mate with either the tubes or chambers inside the muffler. At least one nipple defines the inlet and is connected to the exhaust pipe of the vehicle, while at least one other nipple defines an outlet connectable to the tail pipe. Most prior art mufflers have a single inlet at one longitudinal end of the muffler and a single outlet at the opposed longitudinal end. However, many mufflers include more than one inlet and/or more than one outlet.
The arrangement of tubes and baffles in the prior art muffler depends on the noise characteristics of the engine, the required amount of noise attenuation and the amount of back pressure considered acceptable. A circuitous flow path for the exhaust gases is created by the baffles and tubes to attenuate the engine noise sufficiently without creating too great a back pressure. For example, reversals of the flow of gases could be achieved with the prior art mufflers by extending an inlet tube into a reversing chamber formed by one or more transverse baffles, and by having a return tube communicate with the same reversing chamber. The exhaust gases might thus flow through the inlet tube into the reversing chamber and out the return tube. A second reversing chamber could be disposed at the opposite end of the muffler to enable the exhaust gases to flow from the return tube into the outlet tube of the muffler. A cross flow of the exhaust gases could be achieved by perforating tubes in certain chambers formed by transverse baffles in the muffler. Transverse baffles also could define a resonating chamber into which a tuning tube would extend. The dimensions of the tuning tube and the resonating chamber would be selected to dampen a particular range of frequencies of exhaust gas noises.
One of the more difficult design restraints for exhaust systems is the limited available space on the vehicle. The size and the shape of the available space envelope on the underside of the vehicle invariably affects both the size of the muffler and the possible alignments of the exhaust pipe and tail pipe leading to and from the muffler. In many situations a muffler must be smaller than the available space envelope on the vehicle to allow sufficient room for smooth bends of the pipes leading to or from the opposed heads of the muffler. The reduction in size of the muffler to accommodate the available space on the underside of the vehicle invariably makes the design of the internal components of the muffler more difficult.
Certain vehicles include a convenient space for the transverse mounting of a muffler. However, with the prior art muffler, transverse mounting would require substantial bends in both the exhaust pipe and tail pipe in the vicinity of the muffler. These bends must have a large enough radius to avoid an unacceptable back pressure. However, large bends require additional costly tubing, and must compete for space with other vehicular components.
Certain other vehicles include a convenient space for a muffler just forward of the rear axle. However, the tail pipe extending from the head of prior art muffler to the rear of the vehicle must bend over the top of the rear axle. Thus, the muffler must be spaced a sufficient distance forward of the rear axle to enable the tail pipe to bend upwardly and over the rear axle. As a result, available space forward of the rear axle can not be used by the prior art muffler.
In situations where the available space was especially limited, muffler manufacturers have reinforced sections of the wrapped outer shell of the prior art muffler and formed an aperture through the reinforced portion of the wrapped outer shell. A nipple was then placed in the aperture in the reinforced portion of the wrapped outer shell and welded in position. This nipple typically would extend into a chamber in the muffler. In this type of prior art muffler, one of the opposed heads might be free of apertures extending into the muffler. The additional reinforcing material and the manufacturing steps for reinforcing the outer wrapper, forming an aperture therein and welding the nipple in place, created substantial time and cost penalties for these prior art mufflers. As a result, this prior art muffler was used primarily in isolated instances where all other conventional techniques were unacceptable and where high costs could be tolerated.
Certain mufflers have been manufactured substantially entirely from tubular components. The most common muffler employing all tubular components is referred to as the glass pack muffler, and typically includes a single linear louvered tube extending the length of the muffler and a tubular outer shell surrounding the louvered tube. The tubular outer shell is spaced from the central louvered portion of the tube, but is tightly engaged to the tube adjacent the opposed ends. The space between the louvered portion of the inner tube and the tubular outer shell is filled with a fiberglass material having sound insulating characteristics. Glass pack mufflers typically are employed on high performance cars where it is desirable to minimize back pressure and where higher noise levels are acceptable. U.S. Pat. No. 3,412,825 which issued to James Hall on Nov. 26, 1968 shows a glass pack muffler with the tubes angled relative to the centerline of the muffler to facilitate the connection of the glass pack muffler to the exhaust pipe or tail pipe of the vehicle.
Mufflers consisting entirely of stamp formed components have been designed recently. The typical stamp formed muffler consists of two stamp formed shells which are configured to define a convoluted path through which the exhaust gases must travel. Examples of such stamp formed mufflers include U.S. Pat. No. 2,484,827 which issued to Harley and U.S. Pat. No. 3,638,756 which issued to Thiele. Other stamp formed mufflers have included a plurality of stamp formed components, including a pair of stamp formed outer shells and one or more stamp formed internal components which are intended to create a convoluted path through which the exhaust gases travel. Examples of mufflers of this general type are shown in: British Pat. No. 1,012,463 which issued to Woolgar on Dec. 8, 1965; British Pat. No. 632,013 which issued to White in 1949; U.S. Pat. No. 4,132,286 which issued to Hasui et al on Jan. 2, 1979; U.S. Pat. No. 4,396,090 which issued to Wolfhugel on Aug. 2, 1983; and U.S. Pat. No. 4,456,091 which issued to Blanchot on June 26, 1984.
A particularly desirable muffler formed entirely from stamp formed components is shown in U.S. patent application Ser. No. 934,642 filed Nov. 25, 1986 now U.S. Pat. No. 4,700,806 by Jon Harwood, and is assigned to the assignee of the subject invention. U.S. Pat. No. 4,700,806 shows mufflers formed from a pair of plates that are stamp formed to define channels, portions of which are perforated, and to form at least one tuning tube. The muffler of U.S. Pat. No. 4,700,806 further includes at least one outer shell which is stamp formed to define at least one expansion chamber to surround the perforated channels. Additionally, the stamp forming of the muffler components further defines at least one low frequency resonating chamber which communicates with the tuning tube formed by the stamp formed plates.
All of the above described stamp formed mufflers have been designed with inlets and outlets extending into the opposed longitudinal ends of the muffler. As a result, despite the many advantages of stamp formed mufflers, the known stamp formed mufflers have embodied the same structural limitations as the prior art mufflers having wrapped outer shells. In particular, these known stamp formed mufflers often would require sufficient room for the exhaust pipe and/or tail pipe to undergo one or more large bends to approach the muffler along a line generally parallel to the longitudinal axis of the muffler. As a result, the costs associated with the tubes for such mufflers would be unnecessarily high, and the mufflers often could not make use of all of available space on the vehicle in view of the need to leave room for bends in the exhaust pipe or tail pipe.
In view of the above, it is an object of the subject invention to provide a stamp formed muffler that can substantially facilitate the design and alignment of the exhaust pipe and tail pipe for the vehicle.
Another object of the subject invention is to provide a stamp formed muffler that can accommodate a greater proportion of the available space on the vehicle.
A further object of the subject invention is to provide a stamp formed muffler having an inlet angularly aligned to an outlet thereof to facilitate the connections to exhaust pipes and/or tail pipes.
Still another object of the subject invention is to provide a stamp formed muffler having an inlet or outlet extending through a top or bottom wall of the muffler.
A further object of the subject invention is to provide an exhaust system having a low overall cost.